Messages in this thread Patch in this message | | | Date | Tue, 14 Nov 2023 21:57:12 -0000 | From | "tip-bot2 for Keisuke Nishimura" <> | Subject | [tip: sched/urgent] sched/fair: Fix the decision for load balance |
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The following commit has been merged into the sched/urgent branch of tip:
Commit-ID: 6d7e4782bcf549221b4ccfffec2cf4d1a473f1a3 Gitweb: https://git.kernel.org/tip/6d7e4782bcf549221b4ccfffec2cf4d1a473f1a3 Author: Keisuke Nishimura <keisuke.nishimura@inria.fr> AuthorDate: Tue, 31 Oct 2023 14:38:22 +01:00 Committer: Peter Zijlstra <peterz@infradead.org> CommitterDate: Tue, 14 Nov 2023 22:27:01 +01:00
sched/fair: Fix the decision for load balance
should_we_balance is called for the decision to do load-balancing. When sched ticks invoke this function, only one CPU should return true. However, in the current code, two CPUs can return true. The following situation, where b means busy and i means idle, is an example, because CPU 0 and CPU 2 return true.
[0, 1] [2, 3] b b i b
This fix checks if there exists an idle CPU with busy sibling(s) after looking for a CPU on an idle core. If some idle CPUs with busy siblings are found, just the first one should do load-balancing.
Fixes: b1bfeab9b002 ("sched/fair: Consider the idle state of the whole core for load balance") Signed-off-by: Keisuke Nishimura <keisuke.nishimura@inria.fr> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Chen Yu <yu.c.chen@intel.com> Reviewed-by: Shrikanth Hegde <sshegde@linux.vnet.ibm.com> Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org> Link: https://lkml.kernel.org/r/20231031133821.1570861-1-keisuke.nishimura@inria.fr --- kernel/sched/fair.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 025d909..d7a3c63 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -11184,12 +11184,16 @@ static int should_we_balance(struct lb_env *env) continue; } - /* Are we the first idle CPU? */ + /* + * Are we the first idle core in a non-SMT domain or higher, + * or the first idle CPU in a SMT domain? + */ return cpu == env->dst_cpu; } - if (idle_smt == env->dst_cpu) - return true; + /* Are we the first idle CPU with busy siblings? */ + if (idle_smt != -1) + return idle_smt == env->dst_cpu; /* Are we the first CPU of this group ? */ return group_balance_cpu(sg) == env->dst_cpu;
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